Enamel opacifier and method of using



Patented Jan. 16, 1951 UNITED. STATES ENAMEL OPACIFIER AND METHOD OFUSIN G William J. Baldwin, Snyder, N. Y., assignor, by

mesne assignments, to

National Lead Company,

New York, N. Y., a corporation of New Jersey N Drawing. ApplicationDecember 31, 1946, Serial No. 719,617

The present invention relates to a mill addi--' tion opacifier for usein vitreous enamels and particularly to an opacifier for use withzirconium-opacified frits of the type which develop opacity on heatingin the enameling cycle.

In the enameling of metal and particularly sheet iron and steel, theultimate object is to obtain a vitreous coating upon the metal basewhich presents a high degree of opacity as this is an estheticrequirement in enameling, as great a coverage as possible and a finishedvitreous coating which is resistant to strains and impact incident toassembly, storage, transportation or use.

A very important feature of a finished enamel article and, therefore, ofthe enamel to be applied to the article, is the diffuse reflectance oropacity of the enamel coating. In general, the opacity may be obtainedby adding materials to the glass composing the frit as, for instance,certain compounds of fluorine or antimony, to mention but two of themore popular older types, or zircon as a more recent opacifier. Or,opacifiers may be added to the frit subsequent to its manufacture andmilled therewith as a separate individual ingredient, so-called milladdition opacifiers. ""f 'l Vitreous enamel coatings of exceptionalproperties have been produced in recent years which depend for theiropacity upon the presence of compounds of zirconium in the frit. PatentsNos. 1,944,938 of January 30, 1934, to C. J. Kinzie and 2,326,348 ofAugust 10, 1943, to Frost and Commons relate to enameling or glazingfrit compositions depending upon zircon type opacifiers to obtainrelatively high reflectance values; additional phases of this importantfield are de scribed in patents to Bahnsen et al. Nos. 2,250,456 and2.250.457 of July 29, 1941, and 2,324,812 of July 20, 1943. Frits ofthis type develop opacity in the enameling cycle, in contrast with fritsof other types wherein the opacity is already developed in themanufacture of the frit.

In general, the greater the amount of an opacifier in a frit, the higherthe opacity of the fin- 45 ished enamel; however, it is known that, attimes, surface difficulties in the enamel may be caused by attempts toinclude too great an amount of an opacifier in the frit glass. Thesesurface difficulties decrease the esthetic value of 5 the enamel coatingand, therefore, in effect, defeat one of the purposes of the addition ofthe opacifier. In accordance with the present invention the opacity ofzirconium-opacified enamels of the 5 type which develop opacity onheating the frit during the enameling cycle may have their opacityincreased by the employment of specially prepared opacifiers containingluminum oxide, antimony oxide and phosphorus pentoxide. 6

4 Claims. (Cl. 10648) These special opacifiers are syntheticallyprepared from materials providing aluminum oxide, antimony oxide andphosphorus pentoxide by calcining such materials with the production ofan end product which when finely ground and used as a mill additionincreases the reflectance value of the finished enamel. In Serial No.629,912, filed November 20, 1945, by William J. Baldwin, now Patent No.2,500,231, there is discussed an enamel opacifier containing zirconiumoxide, phosphorus pentoxide and aluminum and, in an application, SerialNo. 716,429, filed December 14, 1946, there is discussed a mill additionopacifier of aluminum oxide and phosphorus pentoxide.

In accordance with the present invention the special mill additionopacifier consisting substantially entirely of phosphorus pentoxide,antimony oxide and aluminum oxide may be prepared by suitably combiningmaterials containing these ingredients or by combining the oxidesthemselves under suitable calcining conditions. Thus, the opacifier maybe prepared from a mixture of suitable raw material containing theoxides mentioned, or of the oxides themselves, by calcining such mixtureat temperatures above about 1600" F. and generally in the neighborhoodof 2000 F., or at such other temperature at which ceramic combination ofthe compounds occurs to produce a relatively homogeneous sinter. Thetime required will be from about hour to about 2 hours. After calciningthe batch, the resultant product is thoroughly pulverized to anappropriate fineness, that is, on the order of to 1 micron, andpreferably as near the lower limit as possible. The product so prepared,when used to the extent of about 2 to 4% as a mill addition to acommercial zirconium opacified frit of the type developing opacityduring the enameling cycle, increased the reflectance value of the finalenamel as compared to the reflectance value of an enamel obtainedwithout the presence of such mill addition material. Ingeneral, thecomposition of the mill addition opacifier of the present inventioncomprises the tertiary system aluminum oxide, antimony oxide andphosphorus pentoxide within the ranges to A1203, 40% to 20% Sb2O3 and40% to 20% P205. One of the molecular formula in 0 this rangecorresponds generally to an empirical oxide formulaof 3A12O3.P2O5.Sb203.

Where the pure oxides are not employed as raw materials from which themill addition of the present invention is manufactured, accepted rawmaterial used in the manufacture of enamel frits will be found suitable,that is to say, amblygonite, aluminum oxide, aluminum metaphosphate orother accepted sources of raw material.

As specific examples merely illu 0 strative of the invention but notlimitative thereof, raw batches were made as shown in the followinexamples by grinding the materials of the raw batch together and heatingthe batch to about 1800" F. for two hours. The product of thecalcination was then ground by wet milling the same untila particle sizeof about 5 microns or less was obtained. Two parts of the resultingground opacifier was added for each 100 parts of frit and milledtherewith, the composition in the mill'being as follows:

100 parts frit 6 parts micronized clay 2 parts special opacifier 0.1part sodium nitrite 42 parts water determined in the usual way by meansof a Hunter 3 Refiectometer. The composition of the samples is given inTable I and the reflectance values are given in Table II.

TABLE I Batch weight and percentage composition of opacz'jiers tested JA B c D E Amblygonite 430 450 560 900 e Alumina Hydrata 430 605 00 153 Ai Qxille 3.93 200. 0 20.0 3 0 A1293 41.5 60.0 25.0 40.0 30. P205" 19.220.0 25.0 40.0 .40. Sb O 39.3 20.0 50.0 20.0 30.

TABLE II Per cent Com osition Reflectance Value at Appli- Oxi e cationWeight No. l

gr./ gr./ gr./ gr./ A1203 Ysbzoa sq. ft. sq. t. sq. ft. sq.ft.

67. 0 72. 7 I 76. 5 78.8 68. O 73. 3 77.2 79. 6 05.0 69.17 73. 2 75. 3G7. 0 72. 4 70. -1 78.4 67.0 71.1 74. 9 77. 4 67.0 71. 8 75. 4 77.6

The milled zirconium-opacified frit having the special mill additionopacifier of the present invention added to it produced an enameledsurface having a considerably greater reflectance at the same rate ofapplication than the frit itself as set forth above in Table II. Thecommercial zirconium-opacified frits of the type which develop 3 opacityduring the enameling' cycle and to which the mill addition opacifiers ofthe present invention may be added with advantage may possess thefollowing approximate composition:

The preferred composition of the special mill addition opacifier of thepresent invention is within the range 40% to 60% A1203, 40% to 20% Sb203and 40% to 20% P205, and one of the compositions corresponds generallyand preferably to an empirical oxide formula (disregardingnon-significant ingredients). Ca1- cined compositions of theseingredients without this range do not produce acceptable reflectancevalues when employed as mill addition opacifiers for zirconium opacifiedfrits of the type that develop opacity in heating, probably by reason ofthe fact that they become soluble in the frit when heated therewithduring the .enameling cycle.

It will be understood that the usual amounts of clay, electrolyte andthe like are added in the mill in the usual way when milling the frit toprepare the enamel slurry.

What is claimed is:

1. The method .of increasing the opacity of an enamel compositioncontaining combined zirconium wherein the opacity is developed onheating in the enameling cycle, which comprises adding 2 to 4% of acalcined product containing A1203, P205 and $10,203 as the essentialingredients and in amounts corresponding essentially to the empiricalformula 3A1203.P205.Sb203, to the enamel composition as .a .milladdition .opacifier and heating to an enamel-forming temperature of 1520C.

2. The method of increasing the opacity of an enamel compositioncontaining combined zirconium wherein the opacity is developed onheating in the .enameling cycle, which comprises adding ,2 to 4% of acalcined product containing A P205, and Sb203 as the essentialingredients in amounts within the range 40% to 60% A1203, 40% to 20%P205 and 40% to 20% .Sb20a, to the enamel composition as a mill additionopacifier and heating to an enamel-forming temperature of 1.52 C.

3,. A mill addition opacifier for enamel compositions of the typecontaining combined zirconium wherein the opacity is developed onheating in the enameling cycle which consists of a calcined productcontaining A1203, P205 andSbzOa as the essential ingredients in amountscorresponding essentially to the empirical molecular formula3A12O3.P2O5.Sb203.

4. A mill addition opacifier for enamel compositions of the typecontaining combined zirconium wherein the opacity is developed onheating in the enameling cycle which consists of a calcined productcontaining A1203, P205 and S1320: as the essential ingredients inamounts in the range 40% to 60% A1203, 40% to 20% P205 and 40% to 20%810203.

WILLIAM J. BALDWIN.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 2,199,794 Harshaw May 7, 19402,252,588 Whitesell Aug. 12, 1941 2,347,187 Frost Apr. 25, 1944

1. THE METHOD OF INCREASING THE OPACITY OF AN ENAMEL COMPOSITIONCONTAINING COMBINED ZIRCONIUM WHEREIN THE OPACITY IS DEVELOPED ONHEATING IN THE ENAMELING CYCLE, WHICH COMPRISES ADDING 2 TO 4% OF ACALCINED PRODUCT CONTAINING AL2O3, P2O5 AND SB2O3 AS THE ESSENTIALINGREDIENTS AND IN AMOUNTS CORRESPONDING ESSENTIALLY TO THE EMPIRICALFORMULA 3AL2O6.P2O5.SB2O3, TO THE ENAMEL COMPOSITION AS A MILL ADDITIONOPACIFIER AND HEATING TO AN ENAMEL-FORMING TEMPERATURE OF 1520* C.